Artificial vegetative propagation
Two main methods;
- taking cuttinggs-a section of stem is cut between lef joints or nodes. The cut end of he stem is then often treated with plant hormones to encourage root growth, and planted. the cuttng forms a new plant which is a clone of the original parent plant. Large numbers of plants, e.g. geraniums, can be produced quickly this way.
- Grafting-a shoot section of a woody plant e.g. fruit tree or rose bush, is joined to an already growing root and stem-rootstock. The graft grows and is genetically identical to the parent plant, but the ROOTSTOCK is genetically DIFFERENT!.
Brambley apple seeds have a genetic mix and will not breed true. So every Brambley apple in the world is a genetically identicalgraft. The graft was first taken in 1856 from a tree in Nottingamshire.
tissue culture->large-scale cloning
cuttings and grafts cannot produce large numbers of clones plants very easily.
some plants do not reproduce well from cuttings or grafts.
More modern methos use plant tissue culture to generate huge numbers of genetically identical plants from a very small amount of plant material.
Tissue culture can be used to generate large stocks of a particularly valuable plant very quickly, with the added advantage that these stocks are known to obe disease-free.
Micropropagation by callus tissue culture
Most common large-scale cloning=micropropagation.
household plants e.g. orchids are produced this way.
- Small piece of tissue is taken from the plant to be cloned, usually from the shoot tip=an EXPLANT.
- the explant is placed on a nutrient growth medium.
- Cells in the tissue divide, but they DO NOT differentiate. Instead they form a mass off undifferentiated cells called a CALLUS.
- After a few weeks, single callus cells can be removed from the mass and placed on a growing medium containing plant hormones that encourage SHOOT GROWTH.
- after a further few weeks, the frowing shoots are transferred to a different growing medium with different hormone concentrations that encourage ROOT GROWTH.
- the growing plants are then transferred into a greenhouse to be acclimatised and grown further before they are planted outside.
Agriculture has sought to provide high-quality crops in terms of yeild and condition resistance e.g. drought or pests. Selective breeding has resulted in crops having reduced genetic variation. Because, farmers have identified and grown only crops with useful features. Some crops e.g. fruit tress, cannot be grown romm a seed because a new tree will have a combination o genes that will not give the correct fruit. Bannas have to be grown through cloning as they are sterile.
Propagation using a callus means;
- farmers know what the crop plant produced will be like, as it is cloned from plants with known features e.g. high yield, taste, colour and disease-resistance-ADVANTAGE
- Farmer's costs are reduced because all the crop is ready for harvest at the same time. ADVANTAGE
This is essentially, a 'REFINEMENT' of selective breeding.
Micropropagation is much FASTER than selective breeding, becuase high numbers can be generate from a small number of parent plants or single valuable plant. ADVANTAGE
Same as those described for asexually reproducing organism;
- genetic uniformity means that all plants are equally susceptible to any new pest, disease or environmental change.
- there is no genetically variety, so parental weaknesses will be in all offspring.
- Striking example=Irish potatoe famine where they lost nearly all potatoe crop as they were all infected with a fungus-like protocists, Pheytophthora infestans. As they were genticall uniform, all were suceptible to the disease.
Now they are regulatedd and the areas given to a specific crop and the distance between areas of the same crop are regulated to limit the effeect of the arrival of new pathogens.